In OFDM WLAN systems, such as those specified by IEEE Standards 802.11a, 802.11g, 802.11n, and 802.16, performance suffers from the presence of a carrier frequency offset. This is due to the fact that the OFDM subcarriers are spaced closely in frequency. Imperfect frequency synchronization causes a loss in subcarrier orthogonality which severely degrades performance.
Referring now to FIG. 1, an OFDM receiver system 10 is shown. Antennas 12-1, 12-2, . . . , and 12-n (referred to collectively as antennas 12) receive signals and pass the signals through low pass filters 14-1, 14-2, . . . , and 14-n (referred to collectively as low pass filters 14). The low pass filters 14 block harmonic emissions which might cause interference with other communications. After being passed through the low pass filters 14, the signals are sent to autocorrelators 16-1, 16-2, . . . , and 16-n (referred to collectively as autocorrelators 16). The autocorrelators 16 find repeating patterns in a signal, such as determining the presence of a periodic signal which has been buried under noise. The signals from the autocorrelators 16 are then combined and sent to a demodulator 18. The demodulator 18 is used to recover the information content from the carrier waves of the signals.